Wide mermaid diagrams are too short

[kenmueller]

Bug Description

Wide mermaid diagrams render too short, causing the text to be very small

Sup AI chat link where the screenshot above is taken: https://sup.ai/chats/ed904061-2e5b-47ca-a36f-28d00acc0bfe

Steps to Reproduce

Normal streamdown with wide mermaid code block

\`\`\`mermaid\nflowchart TD\n    classDef hypo    fill:#6A0DAD,color:#fff,stroke:#4a0080,stroke-width:3px,font-weight:bold\n    classDef ant     fill:#1565C0,color:#fff,stroke:#0D47A1,stroke-width:3px,font-weight:bold\n    classDef post    fill:#BF360C,color:#fff,stroke:#7f2000,stroke-width:3px,font-weight:bold\n    classDef antH    fill:#90CAF9,color:#0D1B2A,stroke:#1565C0,stroke-width:1.5px,font-weight:bold\n    classDef postH   fill:#FFAB91,color:#1a0000,stroke:#BF360C,stroke-width:1.5px,font-weight:bold\n    classDef target  fill:#E8F5E9,color:#1B5E20,stroke:#2E7D32,stroke-width:1.5px\n\n    HYP([\"HYPOTHALAMUS<br/>Master Neuroendocrine Regulator\"]):::hypo\n\n    HYP -->|\"Portal Blood System<br/>Releasing & Inhibiting<br/>Hormones\"| ANT\n\n    HYP -.->|\"Direct Neural Axons<br/>Supraoptic & Para-<br/>ventricular Nuclei\"| POST\n\n    subgraph ANTERIOR_LOBE[\"ANTERIOR PITUITARY (Adenohypophysis)\"]\n        ANT([\"ANTERIOR PITUITARY<br/>Tissue: Glandular Epithelium<br/>Origin: Rathke's Pouch<br/>SYNTHESIZES its own hormones\"]):::ant\n\n        GH([\"GH<br/>Growth Hormone\"]):::antH\n        TSH([\"TSH<br/>Thyroid-Stimulating Hormone\"]):::antH\n        ACTH([\"ACTH<br/>Adrenocorticotropic Hormone\"]):::antH\n        FSH([\"FSH<br/>Follicle-Stimulating Hormone\"]):::antH\n        LH([\"LH<br/>Luteinizing Hormone\"]):::antH\n        PRL([\"Prolactin<br/>PRL\"]):::antH\n    end\n\n    subgraph POSTERIOR_LOBE[\"POSTERIOR PITUITARY (Neurohypophysis)\"]\n        POST([\"POSTERIOR PITUITARY<br/>Tissue: Neural / Glial Pituicytes<br/>Origin: Downgrowth of Hypothalamus<br/>STORES & RELEASES only<br/>hormones made in hypothalamus\"]):::post\n\n        ADH([\"ADH / Vasopressin<br/>Antidiuretic Hormone\"]):::postH\n        OXY([\"Oxytocin<br/>OXT\"]):::postH\n    end\n\n    ANT --> GH & TSH & ACTH & FSH & LH & PRL\n    POST --> ADH & OXY\n\n    GH    --> TGH([\"Bones, Muscles, Liver<br/>Stimulates growth & IGF-1\"]):::target\n    TSH   --> TTSH([\"Thyroid Gland<br/>Releases T3 & T4, regulates metabolism\"]):::target\n    ACTH  --> TACTH([\"Adrenal Cortex<br/>Releases cortisol, stress response\"]):::target\n    FSH   --> TFSH([\"Gonads<br/>Follicle maturation / Spermatogenesis\"]):::target\n    LH    --> TLH([\"Gonads<br/>Ovulation / Testosterone production\"]):::target\n    PRL   --> TPRL([\"Mammary Glands<br/>Milk synthesis & secretion\"]):::target\n    ADH   --> TADH([\"Kidneys & Blood Vessels<br/>Water reabsorption, vasoconstriction\"]):::target\n    OXY   --> TOXY([\"Uterus & Mammary Glands<br/>Contractions, milk ejection, bonding\"]):::target\n\`\`\`

Expected Behavior

Text is a bit larger

Actual Behavior

Text is very small

Code Sample

Streamdown Version

2.5.0

React Version

19.2.4

Node.js Version

14.14.1

Browser(s)

Chrome

Operating System

macOS

Additional Context

No response