You're using Bootstrap.css, which defines a max-width: 540px rule on any element with class="container" when the browser viewport width is wider than 576px:
To fix this, use a different class name other than container, or extend the .container rule in your own stylesheet to set max-width: none;.
But, in my frank opinion, the best solution is to not use Bootstrap.css and to instead take responsibility for styling your own website. I feel Bootstrap has gotten bigger and bigger over the years it takes just as much effort to "learn Bootstrap" as it does to learn how to write one's own base common stylesheet.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
